Drainage pump systems are used to aspirate body liquids and fluids in the medical field. For example, they are used during or after surgical interventions, in wound drainage, in thorax drainage or in liposuction. These drainage pump systems usually have a vacuum pump, one or more fluid collection containers, and a drainage tube connection between patient and fluid collection container. The fluid collection container can be secured releasably on the housing of the drainage pump or connected to the pump via an external vacuum tube.
With an underpressure being generated in the fluid collection container by means of the suction pump or vacuum pump, the fluid or secretion from a cavity in the patient can be aspirated through the drainage or secretion tube and into the collection container and collected therein. Filters arranged on the pump-side outlet of the collection container protect the suction pump from possible contamination by the aspirated fluid. Drainage pump systems of this kind are disclosed in WO 2007/128156 and WO 2008/141471, for example. The drainage pump systems described there are portable.
Capacitive filling level sensors are suitable for the purpose of monitoring the drainage process and the filling level of the fluid collection container.
Filling level sensors are known in the prior art. Thus, U.S. Pat. No. 4,099,167 discloses a capacitive filling level sensor for determining a filling level of a liquid container. In one embodiment, the filling level sensor has a band-shaped first electrode, and several second electrodes spaced apart from the first electrode. The second electrodes are spaced apart from one another in the vertical direction. The first electrode and also the second electrodes are arranged on the outer face of the container. Third band-shaped electrodes are arranged in the horizontal direction inside the container and extend from the first electrode to the second electrodes. In a further embodiment, only the first electrode and the second electrodes are present, the container in this case being designed with a double wall. The first electrode is located on the outer face of the outer wall, and the second electrodes are arranged on the outer face of the inner wall.
U.S. Pat. No. 5,747,689 describes a filling level sensor that is partially immersed in a liquid container. The sensor has two plates extending parallel to each other and spaced apart from each other. One of the plates is segmented, and the individual segments are spaced apart from one another.
JP 2161322 discloses a capacitive filling level sensor with two electrodes, wherein a first electrode is mounted on the outer wall of a container and the second electrode forms a tube piece, through which water flows out of the container.
U.S. Pat. No. 4,092,860 discloses a capacitive filling level sensor mounted on the outer face of a connector piece and composed of several band-shaped electrodes. This sensor is protected from the outside by a Teflon® coating.
DE 196 45 970 discloses a band-shaped capacitive filling level sensor in the form of a flat ribbon cable. The capacitive sensor elements are formed by cores of the flat ribbon cable. The sensor is arranged in the interior of a container.
WO 2009/098077 discloses a capacitive filling level sensor in a measuring container, wherein the sensor comprises segments.
In drainage systems for aspirating body liquids, the filling level sensors are usually located on or in the fluid collection container. Thus, WO 2008/119993 discloses a fluid collection container with a filling level sensor mounted on the outer face of the container. The sensor comprises several band-shaped plates, which are arranged in the vertical and horizontal directions on the container.
EP 0 853 950 discloses a drainage pump unit with a suction unit and with a fluid collection container, where a capacitive filling level sensor is arranged on the suction unit.
For hygiene reasons, fluid collection containers can only be used for a limited time and should therefore be as inexpensive as possible. If the filling level sensors are mounted on the fluid collection container, however, the costs increase. By contrast, filling level sensors mounted on the drainage pump unit have less precision than filling level sensors mounted on the container, particularly in the case of small filling quantities, and particularly in the case of non-homogeneous liquids.